1. Field of the Invention
The present invention relates to a power cord including a plug at a leading end thereof.
2. Description of the Prior Art
One type of conventional power cord includes a plug as described below. Conductors projected (exposed) from leading ends of a plurality of cords are connected to blades. The plug includes an outer skin for covering trailing ends of the blades and the leading ends of the cords. The outer skin is formed of a synthetic resin.
Such a plug has a structure described in, for example, Japanese Laid-Open Patent Publication No. 2003-178835. The plug includes an internal molded body (core), formed of a hard resin, including a plurality of covering and fixing sections. Each covering and fixing section covers a connection part at which the trailing end of each blade is connected to the conductors exposed from the leading end of each cord. The plug also includes an external molded body (outer skin), formed of a soft resin, for covering the covering and fixing sections of the core together.
Such a plug includes the core formed of a soft resin and the outer skin formed of a hard resin. Owing to such a structure, even when a user treats the plug roughly, for example, swings the plug strongly in a direction in which the blades are arranged, the connection parts of the trailing ends of the blades and the conductors are prevented from being broken. Thus, the blades can be displaced with a higher degree of freedom with certainty. In other words, the life of the power cord can be extended by providing the core and the outer skin in the plug.
In the power cord disclosed in the above-identified patent document, the core has a bridge for connecting the covering and fixing sections each for covering the connection part. According to the above-identified patent document, the plug has the following advantages. Even when a strong tensile force or bending stress is applied to the blade/cord connection parts, the bridge alleviates such a force. In addition, the stress applied to the covering and fixing sections by, for example, the bridge being bent is alleviated by the outer skin. As a result, the bending stress applied to the connection parts is reduced. Even when the plug is treated roughly, there is no possibility of breakage of the connection parts.
However, a power cord is occasionally treated more roughly than the plug being swung in the above-mentioned direction. For example, when the user carries an electric appliance including the power cord, the user may hang the power cord on his/her shoulder while holding the plug in his/her hand. In such a case, the blade/cord connection parts are subjected to a stronger tensile force or bending stress than in the case where the plug is swung in the above-mentioned direction.
In the case of a plug as described in the above-identified patent document including a core having a bridge, the applied tensile force or bending stress may exceed the bending limit of the bridge. As a result, the bridge may be broken.
The plug described in the above-identified patent document also has the following drawback. A border part of each cord between a part covered with the covering and fixing section of the core and a part exposed therefrom is not sufficiently reinforced. When the plug is treated excessively roughly, for example, when the user holds the plug in his/her hand while hanging the power cord on his/her shoulder to carry the electric appliance including the power cord as described above, the bending stress is concentrated on the border part due to a significant hardness difference between the core and the cord. This also results in breakage of the cord or conductors.
The present invention has an object of providing a power cord for preventing breakage of a plug or cord/conductors or conductors with certainty even when being treated roughly and thus having a longer life.